Encoded signals that conform to the so-called Dolby Digital Plus standard contain data representing a main audio program and may contain data representing one or more associated audio programs. The Dolby Digital Plus standard is described in Document A/52, “Digital Audio Compression Standard (AC-3, E-AC-3),” Nov. 22, 2010, published by the Advanced Television Systems Committee, Inc. (ATSC), Washington, D.C. The associated audio programs may contain aural content in different languages, vocal commentary on accompanying visual content, or aural content for visually-impaired listeners that describes the accompanying visual content.
The associated audio programs may be mixed with the main audio program during playback of the main audio program and its accompanying visual content. Mixing metadata that is included with an associated audio program specify an amount of attenuation for the main audio program when the associated audio program is mixed with the main audio program.